Wearable sweat lactate monitoring for exercise intensity assessment in cardiac rehabilitation: a proof-of-concept study
J Yamagishi, T Watanabe, S Yuguchi, K Takino, Y Iida, H OkuraAbstract
Background
In patients with heart failure (HF), cardiac rehabilitation (CR) improves exercise capacity, quality of life, and clinical outcomes. Exercise prescription based on the anaerobic threshold (AT) assessed by cardiopulmonary exercise testing (CPET) is recommended in current guidelines. However, shorter hospital stays and limited resources often restrict the availability of CPET, particularly in long-term care hospitals and community settings, making accurate assessment and optimisation of exercise intensity challenging. Concerns regarding exercise safety may therefore contribute to persistently low participation and retention rates in CR. A simple, non-invasive, and safety-oriented method for monitoring exercise intensity is needed. We hypothesised that wearable sweat lactate monitoring could provide a complementary indicator to AT and support safer, more accessible CR.
Methods
This feasibility, proof-of-concept study was conducted at two centres and included fifty healthy volunteers (24 men) as a first step towards application in HF populations. Participants performed a multistage incremental exercise test with 10-watt stepwise increases while wearing a sweat rate monitor and a wearable sweat lactate sensor. Heart rate (HR) and workload (watts) were recorded at the sweat lactate threshold (SLT), defined as the initial sustained rise in sweat lactate concentration, and at points where lactate elevation persisted for 1 minute (SLT-1) and 2 minutes (SLT-2). Standard CPET was performed within one month. Correlations between HR and workload at AT and those at SLT, SLT-1, and SLT-2 were analysed, and agreement was assessed using Bland–Altman analysis.
Results
SLT was identifiable in 43 participants, while SLT-1 and SLT-2 were identifiable in 37. Correlation coefficients with AT were as follows: SLT HR (r = 0.346), SLT workload (r = 0.497), SLT-1 HR (r = 0.453), SLT-1 workload (r = 0.427), SLT-2 HR (r = 0.290), and SLT-2 workload (r = 0.458). The strongest moderate correlation with AT was observed for workload at SLT. Bland–Altman analysis showed a systematic bias with a mean difference of −10.81 watts, indicating that SLT workload occurred at a slightly lower exercise intensity than AT.
Conclusion
This proof-of-concept study shows that wearable sweat lactate monitoring correlates moderately with AT derived from CPET and provides a feasible, non-invasive, and safety-oriented indicator of exercise intensity. Although not intended to replace CPET, this approach may complement conventional assessment and support safer implementation of cardiac rehabilitation, particularly in community-based and remote CR settings for patients with HF. Further validation in HF populations is required.